Thermoplastic vulcanizates (“TPVs”) are vulcanized compositions that include finely dispersed crosslinked elastomeric particles in a continuous thermoplastic phase. TPVs are produced by a process called dynamic vulcanization where the elastomeric component is selectively crosslinked during melt mixing with molten thermoplastics. TPVs have the benefits of the elastomeric properties provided by the elastomer phase and the processability provided by the thermoplastic phase.
Conventional plastic processing equipment can extrude, inject, or otherwise mold, and thus press and shape TPV compositions into useful products alone or in composite structures with other materials. The presence of the dynamically vulcanized, cross-linked rubber particles in TPVs, however, can make these TPVs difficult to process. As a result, the presence of flow marks on the surface of injection molded articles and the presence of surface imperfections on extruded profiles, such as hard spots, die lines, or die deposits, can occur. These surface imperfections on end-use articles are even more visible with soft TPVs and often make existing TPVs unsuitable for many end-use applications, particularly end-use applications where the surface of the finished article is visible, such as extruded weather seals used in automotive applications and different articles made by injection molding, such as soft touch sealing profiles such as glass encapsulations.
Attempts have been made to produce TPVs with improved properties that include blending the TPV with a soft polymer. For example, U.S. Pat. No. 6,288,171 describes TPVs that are blended with a random propylene copolymer in a two-step process and U.S. Pat. No. 7,008,699 describes composite structures where the TPV in the second polymer structure may be optionally blended with a semicrystalline random adhesive copolymer in a two-step process.
Additional attempts have been made to produce TPVs with improved properties by incorporating a second polymer component in the thermoplastic phase of the TPV. For example, U.S. Pat. No. 7,294,675 describes TPVs, where the thermoplastic component comprises greater than 80 wt % of a random propylene copolymer having a melting point of less than 105° C. For example, U.S. Pat. No. 7,326,471 exemplifies TPVs that include 10 to 40 wt % of a second olefinic thermoplastic resin component that has 60 wt % or more units derived from propylene, isotactically arranged propylene derived sequences, and a heat of fusion less than 45 J/g. For example, Japanese Patent Application Publication No. 2014-181266 describes a thermoplastic elastomer composition containing an olefinic rubber (A), an olefinic resin (B) having a melting point of 70 to 200° C., and a propylene-α-olefin random copolymer (C) having a propylene content of 70-90 mol %, a Mw/Mn of less than 3.5, and a melting point of less than 70° C.
Further attempts have been made to produce TPVs with improved properties by using an ultra-fine dispersion of the elastomeric phase within the thermoplastic phase. For example, U.S. Pat. No. 7,829,623 is directed to a method for preparing TPV compositions comprising providing into melt processing equipment (i) from 5 to 10 wt % of at least one thermoplastic polypropylene, (ii) from 6 to 12 wt % of at least one propylene copolymer, and (iii) from 15 to 35 wt % of at least one cross-linkable rubber, where the dispersed, cross-linked phase of the TPV consists of particles having an effective diameter of not greater than 2 millimicrons.
Additional background references include U.S. Pat. Nos. 6,245,856; 6,268,438; 6,399,710; 6,713,520; 7,319,121; 7,964,672; and 8,241,753; U.S. Patent Application Publication No. 2007/0129493; European Patent No. 1655332B1; PCT Publication No. WO 99/27001; and PCT Application No. PCT/CN2013/001634.
Despite these prior attempts, there is still a need for TPVs that have improved processability without sacrificing the mechanical properties of the TPV and that can be used to produce end-use applications that have good surface appearance.